Ken Paxton, the attorney general of Texas, officially announced on Tuesday that he was challenging Senator John Cornyn in the Republican primary next year, setting up what is likely to be the most contentious and expensive intraparty contest of 2026.
Mr. Paxton, a firebrand conservative litigant who has sought to strongly align himself with President Trump, had been teasing a run against Mr. Cornyn for weeks. He all but announced his intentions in an interview with The New York Times last week.
On Tuesday, Mr. Paxton unveiled a website for his nascent campaign, prominently featuring a photo of him posing with Mr. Trump, and he officially announced his run in an interview on Fox News.
“It’s definitely time for a change in Texas,” Mr. Paxton said in the interview with Laura Ingraham. In a post on social media, he promised to “fight for President Trump’s agenda and take a sledgehammer to the D.C. establishment.”
Mr. Paxton has tried to position himself as the preferred candidate of the Republican primary base in Texas, a conservative electorate that has appeared receptive to his campaign in recent polling.
Mr. Cornyn, realizing the looming challenge, announced his own campaign last month in a video that heavily featured his own connections to Mr. Trump. In recent days he rolled out an endorsement from the union for U.S. Border Patrol agents, an important show of support for conservative voters who list border security among their top issues.
In response to Mr. Paxton’s announcement, the Cornyn campaign pointed to the senator’s voting record, which it said aligned with President Trump more than nearly every other senator. The campaign referred to Mr. Paxton as “a fraud.”
“This will be a spirited campaign and we assure Texans they will have a real choice when this race is over,” the campaign said in a statement on Tuesday.
Republican voters in Texas are well familiar with both Mr. Cornyn, who has been in state politics for four decades, and Mr. Paxton, a former state representative and state senator now in his third term as attorney general.
Mr. Paxton survived an impeachment trial in 2023, initiated by Texas House Republicans, over allegations of corruption and abuse of office that were lodged against him by some of his former top aides.
Those aides also filed a whistle-blower suit against him over their firings. Late last week a judge sided with them, saying that Mr. Paxton had admitted to the allegations and that the state should pay $6.6 million to settle the claims. Mr. Paxton has vowed to appeal.